The present invention relates to occupant classification systems.
A capacitive sensing system for a vehicle seat sends a time varying voltage out to a single sensing electrode and measures the loading current to ground from the sensing electrode. The time varying voltage could take many shapes, although a preferred shape is a sinusoidal signal at frequencies between about 50 kHz and about 150 kHz. The loading current increases significantly when an adult occupant is on the seat and only slightly when there is a child seat on the vehicle seat.
Generally, a capacitive sensing system uses one element for both sensing an occupant in a vehicle seat and heating the vehicle seat. Typically, to switch between heating and sensing, high-side and low-side FETs are switched on (heating) and off (sensing) to apply and isolate power and ground respectively. However, one drawback to FETs is that they may have a parasitic capacitance that can affect the sensing measurements.
Accordingly, a system is needed for providing better performance from the inside impedances of the capacitive sensing system.